<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>网页计算器</title>
  </head>
  <body>
    <p>整数1：<input id="num1" type="text"></p>
    <p>整数2：<input id="num2" type="text"></p>
    <p>
      <input type="button" value="相加" onclick="calc(add)">
      <input type="button" value="相减" onclick="calc(sub)">
      <input type="button" value="相乘" onclick="calc(mul)">
      <input type="button" value="相除" onclick="calc(div)">
    </p>
    <p>结果：<input id="result" type="text" readonly></p>
    <script>
      function calc(func) {
        var result = document.getElementById('result');
        var num1 = parseInt(document.getElementById('num1').value);
        var num2 = parseInt(document.getElementById('num2').value);
        if (isNaN(num1) || isNaN(num2)) {
          alert('请输入数字');
          return false;
        }
        result.value = func(num1, num2);
      }
      function add(num1, num2) {    // 加法
        return num1 + num2;
      }
      function sub(num1, num2) {    // 减法
        return num1 - num2;
      }
      function mul(num1, num2) {    // 乘法
        return num1 * num2;
      }
      function div(num1, num2) {    // 除法
        if (num2 === 0) {
          alert('除数不能为0');
          return '';
        }
        return num1 / num2;
      }
    </script>
    <p>
      <a href="file:///C:/Users/rise/Desktop/%E9%A6%96%E9%A1%B5/default/04.html">返回</a>
  </p>
  </body>
</html>